Electrochemical reduction of nitroso compounds: voltammetric, UV–vis and EPR characterization of ortho- and meta-nitrosotoluene derivatives

A comprehensive study of the electrochemical reduction, in different electrolytic media, of two nitroso compounds, i.e. ortho- and meta-nitrosotoluene derivatives has been carried out. Furthermore, UV–vis and EPR spectroscopic characterization of the one-electron reduction product from these derivatives in aprotic media is also reported. Controlled potential electrolysis (CPE) was used to generate the nitroso radical and its detection by cyclic voltammetry, UV–vis and EPR spectroscopy was achieved. In protic media (30% ethanol +0.1 M Britton–Robinson buffer pH 5–12) both derivatives gave a reversible well-defined peak in the whole pH range on Hg in a reaction involving two electrons to give the hydroxylamine derivative. In mixed aqueous organic media (0.015 M aqueous citrate+DMF: 40:60 and 0.1 M TBAI) at pH>8 isolation and electrochemical characterization of the nitroso radical anion was achieved. Under these experimental conditions, nitroso derivatives are reduced in a quasi-irreversible mechanism. In aprotic media (0.1 M TBAI in DMF), the nitroso radical anions decay by a dimerization, with rate constant values, k2,: 4100±52 (M s)−1 and 2700±28 (M s)−1 for ortho- and meta- nitrosotoluene, respectively. The proposed electroreduction mechanism of the nitroso derivatives were supported by digital simulation through a digisim 2.1 software version.